1. Technical Field
The present invention relates generally to a vehicle tire. In particular, the present invention relates to a tread pattern for the tire. The tread pattern generates a comparatively reduced level of noise during rotation of the tire on a road surface.
2. Description of the Prior Art
When a vehicle tire rotates on a road surface during operation, it is known that noise is generated. This is referred to as "tire/road noise" but will simply be referred to herein as "noise". The noise can be objectionable to an occupant inside of the vehicle or to a person located outside near the vehicle. The noise is generally attributed to the leading edge of each individual tread element of the tire impacting the road surface during rotation of the tire. Each impact disturbs the air surrounding the tread element and the tire. The additive effect of these repeated air disturbances is sound energy which has amplitude and frequency characteristics.
Reducing such noise has become important with the advent of the increasingly popular "all season" tire and with the introduction of legislation which limits noise emanating from operating vehicle tires. The all season tire has a plurality of tread elements arranged circumferentially in a spaced relationship about the tire and extending radially therefrom. The tread elements have a pitch length which is taken in the circumferential direction about the tire. Tire designers have attempted to reduce the amplitude of the sound energy or to spread the sound energy over a relatively wide spectrum of audible frequencies to approach what is commonly referred to as "white noise" which is relatively innocuous or less objectionable.
Tire designers have varied the pitch length ratio and/or the circumferential sequencing of adjacent tread elements. For example, U.S. Pat. No. 3,989,780 discloses a tire tread pattern with varied pitch length ratios between adjacent tread elements. Relatively high pitch length ratios can often lead to malwear of the tread elements. U.S. Pat. No. 4,474,223 discloses modifying the generation of noise in a rotating tire by sequencing a number of repeating design cycles. The sequencing is done according to a predetermined mathematical formula. However, further reduction in noise generated by a tire rotating on a road surface is continually being sought by tire manufacturers.